Method of treating cardiovascular disease by angiogenesis

ABSTRACT

A system and method for treating cardiovascular disease utilizes electromagnetic fields (EMF) applied by non-invasive or minimally invasive procedures. The EMF is applied to existing vascular structure to modulate blood flow and blood vessel growth in the patient. In one embodiment, a structure of electromagnetic coils is placed about a desired treatment zone to apply an EMF to the zone on the order of 10 4 -10 T. For cardiac angiogenesis, coils can be positioned on the anterior chest wall and on the back at the level of the heart. Various coil configurations are contemplated to yield appropriate field intensities at the treatment zone. In another embodiment, coils can be implanted within the patient and placed within or overlying the treatment zone incorporating several aspects, such as frequency components, the use of ca carrier frequency, pulse shape, duty cycle, and total time exposure to the EMF.

This application is a continuation of application Ser. No. 09/325,229filed on Jun. 3, 1999 now U.S. Pat. No 6,200,259.

The present invention is directed to a method for treatingcardiovascular disease by promoting growth of collateral vessels toincrease blood flow to target organs and tissues.

BACKGROUND OF THE INVENTION

The major component of morbidity and mortality attributable tocardiovascular disease occurs as a consequence of the partial orcomplete blockage of vessels carrying blood in the coronary vascularsystem and in peripheral vasculature. When such vessels are occluded,various clinical syndromes may result from death of tissue previouslynourished by the occluded vessels or inability of the vessels totransport sufficient blood supply to regions requiring high bloodconsumption and accompanying nutrients. In some individuals, bloodvessel occlusion is partially compensated by the natural process ofangiogenesis, in which new conduits are formed to replace the functionof the impaired vessels. These new conduits, called “collateral”vessels, may facilitate restoration of blood flow to the deprivedtissue, thereby constituting “natural bypasses” around the occludedvessels. However, some individuals are unable to generate sufficientcollateral vessels to manage the consequences of diminished blood flowfrom cardiovascular disease.

At present, blood vessel occlusions are usually treated by mechanicallyenhancing blood flow or by medical reduction of oxygen demands in theinvolved tissues or organs. Mechanical enhancements are provided mostcommonly by (1) employing surgical techniques that attach autologous orsynthetic vascular conduits proximal and distal to the areas ofocclusion, thereby providing bypass grafts, or (2) revascularization byvarious means to physically enlarge the vascular lumen at the site ofocclusion. These procedures involve such devices as balloons,endovascular knives (atherectomy), endovascular drills, and the like.The surgical approach is accompanied by significant morbidity and evenmortality, while the angioplasty-type processes are complicated byrecurrent stenoses in 25-35% of cases. Successful mechanicalrevascularization depends, inter alia on accessibility of the occludingstenosis to such procedures. Clearly, there remains a pressing need formeans to stimulate angiogenesis to provide collateral blood flow bynon-invasive or minimally invasive procedures.

SUMMARY OF THE INVENTION

This invention employs electromagnetic fields (EMF) applied bynon-invasive or minimally invasive procedures to modulate blood vesselgrowth in human or animal vasculature. In positive modulation, externalapplication of energy fields stimulates progressive collateralization byartificially inducing or enhancing biochemical and cellular responses inthe tissues permeating the target fields. In this manner, blood flow isrestored to coronary and other organ systems, peripheral vasculature andmuscle vascular beds through an accelerated formation and/or maturationof newly-generated and enlarged vessels that bypass partially orentirely occluded vasculature by induced angiogenesis.

From a clinical perspective, the choice to use such non-invasiverevascularization would be particularly appropriate (1) in patientswithout reasonable options for mechanical revascularization because ofinaccessible location of the stenosis, diffuse vascular disease, or pooroverall medical condition for surgical or even endovascularintervention; (2) as an adjunct to surgical or endovascularinterventions, in which the anatomy of the patient's blood vesselsprecluded revascularization of all ischemic regions (i.e., incompleterevascularization using other modalities); (3) as an adjunct to theapplication of other mechanical stimuli such as laser channel formation(transmyocardial laser revascularization) which have been found toreduce symptoms of ischemia; (4) as an adjunct to the administration ordirect application of genetic or growth factor agents also intended tofacilitate vascular growth or angiogenesis; and (5) in patients withischemic disease and attendant symptoms who are not yet appropriatecandidates for the above interventions, thereby favoring a non-invasiveprocedure and making possible earlier therapy attended by virtualabsence of morbidity.

Potential forms of energy fields include electromagnetic fields that arepulsed over a wide range of frequencies, intensities and pulsed waveformshapes (PEMF). Electromagnetic fields may also be generated in acontinuously oscillating, non-pulsed manner, thus providing a sinusoidalwaveform. Specific combinations of these variables deliver a range ofbiological effects that can be tailored to desired results. Other energyforms, including pulsed or continuously-generated microwave-radiatedenergy and ultrasonic energy, may be applied. In the case of PEMF,application involves placement of coils around the regions of tissues inwhich collateralization is desired. One approach is to embed the coilsin a cloth wrap, which may be worn as a garment surrounding the bodyarea of interest. For cardiac applications, a vest-type garment may befabricated. For peripheral applications a wrap, i.e., either around theleg or arm, can be designed to deliver the desired field to the affectedorgan or tissue.

The structure of coils contained within such garments or wraps canprovide for simple homogeneous, “flat” field distributions inthree-dimensional space, or may be configured to focus on fields withgreater intensity localized near the target area.

The number of wire loops comprising a single coil, or each of severalcoils, and the electric power used to power these wire loops, should besuch that the peak intensity of the field within the region of interestis on the order of 10⁻⁴-10 T.

These applications of energy fields may be utilized not only as primarytherapy but in conjunction with mechanical approaches torevascularization or following standard surgical/endovascular orangioplasty approaches. For example, where such revascularization ispartially but inadequately achieved by standard techniques,externally-based fields provide an opportunity for complementaryrevascularization of target areas.

Apparatus for delivering the desired electromagnetic stimulation totarget areas taught herein are readily adapted from well-reported (EMF)technology relating to the skeletal system. Principles of design are tobe found, for example, in U.S. Pat. Nos. 4,266,532, 3,890,953 and3,915,151. This applies not only to the basic structure employed in thedelivery system but also for the ranges of parameters, as discussedherein. Of particular interest for its comprehensive coverage ofelectromagnetic therapy is Bassett, “Fundamental and Practical Aspectsof Therapeutic Uses of Pulsed Electromagnetic Fields (PEMFs),” CriticalReviews in Biomedical Engineering, 17:451, Issue 5 (1989). Also ofinterest in refining parameters based on target location andenvironment, are the following: Norton, “Pulsed Electromagnetic FieldEffects on Chondroblast Culture,” Reconstr. Surg. Tramaut., 19:70(1985); Detlavs et al., “Experimental Study of the Effects ofRadiofrequency Electromagnetic Fields on Animals With Soft TissueWounds,” Sci. of Total Environ., 180:35 (1996); Lin et al., “Effects ofPulsing Electromagnetic Fields on the Ligament Healing in Rabbits,” J.Vet. Med. Sci. 54(5):1017 (1992); Goats, “PulsedElectromagnetic-(short-wave) Energy Therapy,” Br. J. Sp. Med. 23:213;Glassman et al., “Effect of External Pulsing Electromagnetic Fields onthe Healing of Soft Tissue,” Annals of Plast. Surg. 16(4):287 (April1986); Watkins et al., “Healing of Surgically Created Defects in theEquine Superficial Digital Flexor Tendon: Effects of PulsingElectromagnetic Field Therapy on Collagen-type Transformation and TissueMorphologic Reorganization,” Am. J. Vet. Res. 46(10):2097 (1985), andZoltan, “Electrical Stimulation of Bone: An Overview,” Seminars inOrthopaedics 1(4):242 (1986).

The use of PEMF and local application of ultrasonic energy have beendescribed as providing enhancement of fusion rates of bony fractures, aswell as accelerating rates of wound healing. U.S. Pat. No. 5,524,624.Such procedures have shown significant promise in diabetes, tobacco use,or other conditions which appear to deter natural bone healing or woundhealing responses. They have, however, suggested no extension of theelectromagnetic phenomenon in circumstances where positive or negativemodulation of angiogenesis can provide dramatic opportunities foraddressing problems of (1) occlusions in the coronary and other organsystems and peripheral vasculature, and (2) blood-dependent tumoroustissues.

DESCRIPTION OF THE FIGURES

FIGS. 1A-1C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with anterior and posteriorcoils in accordance with one embodiment of the present invention.

FIGS. 2A-2C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with an anterior coil only inaccordance with a further embodiment of the present invention.

FIGS. 3A-3C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with coil having a bent ovalconfiguration in accordance with another embodiment of the presentinvention.

FIGS. 4A-4C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with an anterior coil and alarger posterior coil in accordance with yet another embodiment of thepresent invention.

FIGS. 5A-5C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with two sets of coils inaccordance with an alternative embodiment of the present invention.

FIGS. 6A-6C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with coils verticallypositioned adjacent the pericardial sac in accordance with an additionalembodiment of the present invention.

FIGS. 7A-7C are diagrammatic representations of anterior, side andposterior views of a human heart and torso with coils horizontallypositioned adjacent the pericardial sac in accordance with an additionalembodiment of the present invention.

GENERAL DESCRIPTION

It is important, in the application of electromagnetic fields tofacilitate or prevent angiogenesis, that the body's region of interestbe subjected to an essentially homogeneous electrical field for maximumefficacy and safety. This means that the treatment field should havespecific spatial and temporal characteristics. To achieve this focusedtreatment environment with deep tissue penetration, pulsed EMF ispreferred.

Spatial Characteristics

An apparatus is designed to deliver PEMF with the appropriate spatialcharacteristics for treatment of the region of focus in threedimensions. For example, the field must be sufficiently homogeneous withrespect to biological effects throughout the cardiac volume in the caseof coronary angiogenesis or other target areas.

A degree of spatial specificity is assured by the fact that ischemictissues possess increased sensitivity to a variety of proangiogenicstimuli. Accordingly, regions of the muscle or surrounding organs whichare not actively ischemic by virtue of limited blood flow would not beexpected to respond to PEMF as readily as ischemic tissues. In ischemictissues, a variety of other receptor and growth factor gene expressionsoccur in response to the ischemia, thereby conferring enhancedsensitivity on the field. High resolution of the spatial characteristicsof the field to restrict exposure to target tissues are usually notnecessary. Instead, it is sufficient that adequate field amplitude bedirected to the target region to provide a stimulus that is greater thana threshold required to yield a desired biologic response.

One approach for providing the desired PEMF signal to the target tissuevolume, either including the heart, or peripheral musculature, is theuse of paired (Helmholtz) coils which are placed in a parallelconfiguration separated by a distance approximately similar to thediameter of the coils, so that the space between the coils encompassesthe target volume for treatment. The coils are then energizedsimultaneously. This arrangement results in a substantially homogeneousfield within the target volume, which will thus produce biologicallysignificant effects therein. For cardiac angiogenesis, coils would bepositioned on the anterior chest wall and on the back, at the level ofthe heart.

FIG. 1 depicts a human torso containing a heart. FIG. 1A shows anterior1 and posterior 2 coils as described, with diameters slightly largerthan cardiac silhouette 3, and similar to the anterior-posteriordistance between the two coils. FIG. 1B, with the arm raised,demonstrates that the anterior 1 and the posterior 2 coils are placed soas to encompass the cardiac region in the volume subtended by the twocoils. FIG. 1C shows posterior coil 2, again with diameter similar tothat of anterior coil 1 and to the distance separating the two coils.FIG. 1B also shows a pulse generator box 4, consisting of a powersupply, an appropriate circuitry designed to generate pulses to energizethe coils, and an amplifier apparatus as necessary to amplify thesepulses to the desired energies. Also shown in FIG. 1B are leads 5running from the pulse generator/amplifier circuitry box 4 to the pairedcoils 1 and 2. The generator box 4 and leads 5 are present but not shownin FIGS. 2-7.

Where less field homogeneity is required for the treatment of the targetvolume, a single coil on the anterior or posterior surface of the thoraxmay be used. Such a coil provides a field of an intensity that decreasesas the distance from the surface of the coil increases. This simplerapproach is feasible because it has been determined that the biologicaleffects of PEMF are relatively amplitude-insensitive. In that case, thedecrement and intensity distance from the coil may be comparativelyunimportant to achieve the desired effect.

FIG. 2 depicts a single coil 1, placed on the anterior aspect of thechest, again with diameter so it would be greater than that of thecardiac silhouette.

To enhance focus of PEMF intensity in the cardiac region, an asymmetricconfiguration comprising a bent oval wrapped from the anterior thoraxalong the left side of the body may be used to encompass within itsfield a geometric space that includes the heart.

FIG. 3 depicts a bent oval configuration for the single coil 1, whichprovides a wrap extending from the anterior view in FIG. 3A, around theleft aspect of the thorax as seen in FIG. 3B, and onto the back as inFIG. 3C, thus encompassing the heart volume within its bent shape.

Another means for enhancing field focus is to provide intensity andspecificity in the cardiac region by a comparatively small anterior coiland a comparatively large posterior coil, causing the moreanteriorly-located heart to receive the greater intensity of fieldstrength.

FIG. 4 demonstrates a comparatively small anterior coil 1 positionedover the heart, thus providing for an increase in the volume-specificfield intensity in the anterior aspect of the thorax, closer to thelocation of the cardiac volume. FIG. 4C also shows this smaller coil 1placed anteriorly and a larger coil 2 placed posteriorly. FIG. 4Bfurther shows larger coil 1, which produces a diminished field intensityas the back is approached.

Enhanced PEMF effects in the cardiac region in comparison to other areasof the thorax may also be provided by intermittent application of a PEMFusing anterior and posterior coils alternating with PEMF employing leftand right-sided coil placements. Here, the fields with alternateinteraction from the anterior-posterior and the side-to-side directionprovide a convergence of both fields upon the cardiac volume. Tissues onthe left or right or anterior and posterior to the heart would receiveless intense fields because they would not be at the intersection of the“field cylinders.”

FIG. 5 shows two pairs of coils, with an anterior 6 and posterior 7 pairof coils, respectively, in the anterior and posterior views in FIGS. 5Aand 5C, and a left/right pair of coils 8 seen both from the front andback in FIGS. 5A and 5C. The left coil is best seen in FIG. 5B. Thesewould be energized so that the anterior/posterior pair would initiallycreate a field, alternating with a field created between the left andright pair of coils. Accordingly, the tissue volume that would receivethe maximal energy exposure would be the cardiac volume occurring at theintersection of the cylinders described by the two coil pairs in FIGS.5A and 5C. FIG. 6 shows a pair of coils implanted either within oroverlying the pericardial sac for maximal spacial proximity to thecardiac tissue.

Enhanced spatial localization of the PEMF to the region of the heart mayalso be achieved while limiting exposure of other tissues by use of asingle coil, or one or both of a pair of coils placed in the body bysurgical or minimally-invasive methods. One or more such cells areplaced in geometric proximity to the cardiac structure. Such coils wouldpreferably be in opposition to the heart surface, either outside orinside the pericardial space. In this way, the heart structures wouldreceive the maximum geometrically feasible localization as compared tothe adjacent thoracic structures.

FIG. 6 shows coils 8 and 9 placed in a vertical plane, seen both fromthe anterior and back views in FIGS. 6A and 6C, as well as in FIG. 6B.

Further shaping of the PEMF field in three dimensions is possible byutilizing structures of variable permeability to the electromagneticfields placed as specific shields on the thoracic body wall, inconjunction with coils similarly placed. These shields, consisting ofthin (1-100 micron) layers of material incorporating ferromagnetic orother similar materials, would be placed between the coil surfaces andthe body wall. Selective placement of such shields makes it possible tofocus the field intensity on the desired tissue volume while diminishingits intensity in other regions.

FIG. 7 depicts an alternative positioning for implanted coils to beplaced within or overlying the pericardial sac, in the horizontal plane.In FIG. 7, two coils 10 and 11 are seen encircling the heart at its base(the lower portion), as well as at its apex (the upper portion). Thesecoils may be seen from the front, (FIG. 7A), left (FIG. 7B) and back(FIG. 7C) to encircle the cardiac volume.

Temporal Characteristics

The temporal characteristics of a PEMF dosage plan includes severalaspects: (1) individual frequency components of the employed fields, (2)the presence or absence of a “carrier” frequency which may be modulatedwith a frequency of lower value; for example, a carrier frequency of 100KHz-10 GHz might be modulated or pulsed with a frequency of 20-10,000Hz, (3) the particular shape of the pulses, expressed as electromagneticenergy varying with time, (4) the “duty cycle” of the pulsing field,i.e., whether the variable fields are applied continuously or in “burst”patterns with intermittent periods of no electrical fields, (5) thetotal time of bodily exposure to the field-generating device on a dailybasis, and (6) the number of days over which the device is to beutilized in a treatment plan. Several of these variables have preferredranges which have been defined by observation of biological responsesboth in vitro and in vivo.

Alternatively, dual or multiple sinusoidal frequencies in a serial orparallel combination may be provided as non-sinusoidal pulse wave formswhich may be square, triangular, or intermediate in shape. Suchnon-sinusoidal wave forms contain within them a variety of frequencieswhich comprise the overall shape, as defined by a Fourier transform,revealing contained frequency components of simple sinusoidalfrequencies. Accordingly, a single repetition rate of a non-sinusoidalwave-form can contain numerous inherent sinusoidal frequency components,and a range of frequencies within this domain of frequencies thusprovides an efficacious biological response. Such pulsed wave-forms aretypically employed at repetition rates within the range of 20-4,000hertz but may incorporate frequency components up to 10 GHz. To conserveenergy from portable batteries or power pack systems, limited dutycycles of the pulsed field are employed for periods of time from 10-100%of total time. Time or exposure to the device ranges from 1-24 hours perday, preferably from about 1-6 hours per day.

Preferred Embodiment

A device for treatment of the coronary vasculature comprises a thinlyconfigured set of coils and power supply sufficiently compact to be wornunderneath clothing, either while the patient is ambulatory and activeor at rest. Each of a pair of coils is positioned anterior and posteriorto the region requiring angiogenic facilitation of cardiac vessels ortissues. Optimal positioning of the coils is slightly left of midline onthe anterior chest wall and on the back, at the level of the heart.Diameters of these coils range approximately from 10-15 centimeters.However, they may be smaller, or, in fact, encompass virtually theentire chest. Homogeneity of the electric field intensity is obtainedfor pairs of coils when spaced at a coil separation approximating thediameter of the coils. Accordingly, one optimal coil diameter isconfigured to the anterior-posterior thickness of the subject's chest. Areasonably homogeneous field would thereby be provided to the entirecardiac tissue volume.

The coils are comprised of wire wrappings providing peak magnetic fieldsof 10 μT-5 T, as measured in the treatment region between the coils whenenergized. These wire wrappings are placed within a thin, flexiblecontaining material such as of plastic, cloth, or rubber which may beworn on the body underneath clothing, with a minimum of discomfort. Thecoils are connected by power supply wires to a pulse generator which isalso worn beneath the clothes, and may be placed in apposition to one ofthe coils. The pulse generator is energized during the time periods oftreatment, typically 1-16 hrs/day, especially 1-4 hrs/day, and providesenergy to the coils with a temporal configuration which results inpositive vascular growth modulation. Such signals may be pulsed withrepetition rates of 20-4000 Hz, with emissions of bursts of pulsesoccurring 1-50 times each second. The pulse bursts may include from10-100 discrete pulses, or alternatively the pulses may be providedthroughout the time period, without a burst timing. The pulse generatormay be programmed for the desired treatment modality to be automaticallyprovided for the selected time period, once activated by the patient,with a mechanism to ensure power-down at the correct time.

In like manner, the methods of this invention may be adapted by thoseskilled in the arts involved to treat blockages of vessels in theperipheral vasculature by noninvasive or minimally-invasive procedures.

What is claimed is:
 1. A method for modulating blood vessel growth intargeted coronary or peripheral vasculature comprising: applying anelectromagnetic force (EMF) to the desired treatment zone to modifyblood flow thereto.
 2. A method for modifying blood flow in targetedcoronary vasculature comprising: applying an electromagnetic field (EMF)to the desired treatment zone to modulate blood vessel growth thereto inwhich the EMF is induced by pulsed DC or AC current.
 3. The method ofclaim 2 in which EMF is applied in conjunction with mechanicalrevascularization.
 4. The method of claim 3 in which EMF is applied inconjunction with angioplasty.
 5. The method of claim 2 in which EMF isapplied in conjunction with administration or direct application ofgenetic or growth factor agents to facilitate vascular growth orangiogenesis.
 6. The method of claim 2 in which EMF is applied inconjunction with transmyocardial mechanical or laser revascularization.7. A method for modulating blood vessel growth in targeted peripheralvasculature comprising: applying an electromagnetic force (EMF) to thedesired treatment zone to modify blood flow thereto in which the EMF isinduced by pulsed DC or AC current.
 8. The method of claim 7 in whichEMF is applied in conjunction with mechanical revascularization.
 9. Themethod of claim 8 in which EMF is applied in conjunction withangioplasty.
 10. The method of claim 7 in which EMF is applied inconjunction with administration or direct application of genetic orgrowth factor agents to facilitate vascular growth or angiogenesis. 11.A method for modifying blood flow in targeted coronary or peripheralvasculature comprising: applying an electromagnetic force (EMF) to thedesired treatment zone to modulate blood vessel growth.
 12. The methodfor modifying blood flow of claim 11, wherein the EMF is induced bypulsed DC or AC current.
 13. The method of claim 11 in which EMF isapplied in conjunction with mechanical revascularization.
 14. The methodof claim 11 in which EMF is applied in conjunction with angioplasty. 15.The method of claim 11 in which EMF is applied in conjunction withadministration or direct application of genetic or growth factor agentsto facilitate vascular growth or angiogenesis.